In Stevens U.S. Pat. Nos. 3,485,234 and 3,585,707, tubular products such as catheters are disclosed which comprise an extruded plastic coating having a tubular, braided wire sheath disposed tightly about a plastic coating in telescoping relation therewith. A second, extruded layer of plastic is then applied over the braided sheath.
Such a catheter having a braided sheath increases the torsional stiffness of the catheter, so that torque may be better transmitted to typically the distal tip thereof with manipulation from the proximal catheter end. Such a characteristic is desirable to facilitate advancement, for example of an intravascular catheter through the branching blood vessel system of a patient. As the catheter is advanced, the surgeon may rotate the proximal end, and, by the invention of the Stevens patents, the distal end more accurately follows the desired rotational movement imparted to the catheter by the surgeon.
In some uses, it would be desirable for certain portions of the catheter to have more or less torsional rigidity than other portions of the catheter. For example, it might be desirable for the distal tip of the catheter to be very soft and pliable, with a low torsional rigidity, while an intermediate section of the catheter should have greater amounts of torsional rigidity to permit the transfer of torque to the tip area from the distal end.
On the other hand, it may be desirable for a catheter to have high torque at its tip but low longitudinal stiffness or "pushability". On the other hand, other sections such as the hub may desirably have high "pushability" or longitudinal rigidity, but with less torsional rigidity. Other sections of the catheter may desirably have intermediate properties in terms of torsional and longitudinal rigidity or stiffness.
By this invention, varying sections of the catheter may have varying torsional and longitudinal rigidity, in accordance with many different, desired, predetermined plans. This may be accomplished by variation of the relationships of the strands in the flexible, tubular, braided wire sheath provided to the catheter, to provide catheters with varying properties as may be desired.